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Commit 40463336 authored by Tom Cherry's avatar Tom Cherry
Browse files

init: use an eventfd instead of socketpair to wake the main loop 

eventfd is a more suitable mechanism.

Bug: 150863651
Test: boot CF, ctl.start services, reboot CF
Change-Id: Ie5c3b0c048afdd7afa4bfc4cba26bec3225925e5
parent 919678bc

init/init.cpp

+18 −21
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ 
#include <signal.h>

#include <stdlib.h>

#include <string.h>

#include <sys/eventfd.h>

#include <sys/mount.h>

#include <sys/signalfd.h>

#include <sys/types.h>
@@ -115,30 +116,26 @@ static std::queue<PendingControlMessage> pending_control_messages; 
// to fill that socket and deadlock the system.  Now we use locks to handle the property changes

// directly in the property thread, however we still must wake the epoll to inform init that there

// is a change to process, so we use this FD.  It is non-blocking, since we do not care how many

// times WakeEpoll() is called, only that the epoll will wake.

static int wake_epoll_fd = -1;

// times WakeMainInitThread() is called, only that the epoll will wake.

static int wake_main_thread_fd = -1;

static void InstallInitNotifier(Epoll* epoll) {

    int sockets[2];

    if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0, sockets) != 0) {

        PLOG(FATAL) << "Failed to socketpair() between property_service and init";

    }

    int epoll_fd = sockets[0];

    wake_epoll_fd = sockets[1];



    auto drain_socket = [epoll_fd] {

        char buf[512];

        while (read(epoll_fd, buf, sizeof(buf)) > 0) {

    wake_main_thread_fd = eventfd(0, EFD_CLOEXEC);

    if (wake_main_thread_fd == -1) {

        PLOG(FATAL) << "Failed to create eventfd for waking init";

    }

    auto clear_eventfd = [] {

        uint64_t counter;

        TEMP_FAILURE_RETRY(read(wake_main_thread_fd, &counter, sizeof(counter)));

    };



    if (auto result = epoll->RegisterHandler(epoll_fd, drain_socket); !result.ok()) {

    if (auto result = epoll->RegisterHandler(wake_main_thread_fd, clear_eventfd); !result.ok()) {

        LOG(FATAL) << result.error();

    }

}



static void WakeEpoll() {

    constexpr char value[] = "1";

    TEMP_FAILURE_RETRY(write(wake_epoll_fd, value, sizeof(value)));

static void WakeMainInitThread() {

    uint64_t counter = 1;

    TEMP_FAILURE_RETRY(write(wake_main_thread_fd, &counter, sizeof(counter)));

}



static class PropWaiterState {
@@ -182,7 +179,7 @@ static class PropWaiterState { 
                LOG(INFO) << "Wait for property '" << wait_prop_name_ << "=" << wait_prop_value_

                          << "' took " << *waiting_for_prop_;

                ResetWaitForPropLocked();

                WakeEpoll();

                WakeMainInitThread();

            }

        }

    }
@@ -249,7 +246,7 @@ static class ShutdownState { 
        }

        shutdown_command_ = command;

        do_shutdown_ = true;

        WakeEpoll();

        WakeMainInitThread();

    }



    std::optional<std::string> CheckShutdown() {
@@ -333,7 +330,7 @@ void PropertyChanged(const std::string& name, const std::string& value) { 


    if (property_triggers_enabled) {

        ActionManager::GetInstance().QueuePropertyChange(name, value);

        WakeEpoll();

        WakeMainInitThread();

    }



    prop_waiter_state.CheckAndResetWait(name, value);
@@ -459,7 +456,7 @@ bool QueueControlMessage(const std::string& message, const std::string& name, pi 
        return false;

    }

    pending_control_messages.push({message, name, pid, fd});

    WakeEpoll();

    WakeMainInitThread();

    return true;

}
@@ -485,7 +482,7 @@ static void HandleControlMessages() { 
    }

    // If we still have items to process, make sure we wake back up to do so.

    if (!pending_control_messages.empty()) {

        WakeEpoll();

        WakeMainInitThread();

    }

}